This book constitutes the refereed proceedings of the 6th International Conference on Extending Database Technology, EDBT '98, held in Valencia, Spain, in March 1998. The 32 revised full papers presented together with one invited keynote were selected from a total of 191 submissions. The book is divided in sections on similarity search and indexing, query optimization on the Web, Algorithms for data mining, modelling in OLAP, query processing and storage management, aggregation and summary data, object-oriented and active databases, view maintenance and integrity, databases and the Web, workflow and scientific databases.